"Reflection Pond" by U.S. National Park Service , public domain
![]() | DenaliGeology Road Guide |
Geology Road Guide to Denali National Park & Preserve (NP&PRES) in Alaska. Published by the National Park Service (NPS).
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National Park Service
U.S. Department of the Interior
Denali National Park & Preserve
geology road guide
Denali National Park & Preserve
geology road guide
Capps . McLane . Chang . Grover . Strand
Credits
Former Denali geologist Phil Brease initiated this guide for the benefit of
countless future staff and visitors. It is the product of multiple years’ worth of
efforts by National Park Service (NPS) staff and Geological Society of America
(GSA) interns.
Authors
Denny Capps, NPS Geologist, Denali National Park and Preserve
Sierra McLane, NPS Director, Murie Science and Learning Center
Lucy Chang, GSA Intern, Geoscientists-in-the-Parks program
Layout and Design
Ellen Grover, NPS Science Communicator, Denali National Park and Preserve
Sarah Strand, GSA Intern, Geoscientists-in-the-Parks program
Laura Vachula, NPS Education Technician, Denali National Park Preserve
Special Thanks
Christina Forbes, GSA Intern, Geoscientists-in-the-Parks program
Chad Hults, Don and Sandy Kewman, Jan Tomsen, Kara Lewandowski,
Ron Cole, and other contributers and reviewers
Cover Photo
NPS Photo / Tim Rains
How to Cite This Book:
Capps, D., McLane, S., and Chang, L. 2020. Denali National Park and Preserve
Geology Road Guide (3rd ed.). National Park Service, Denali National Park and
Preserve, Denali Park, Alaska.
Available for free online.
The original edition of this book was inspired by the 2016 National Park Service
Centennial during which Denali celebrated 100 years of geological research and
exploration.
C016245
Dedication
This guide is dedicated to Phil Brease (Denali Park Geologist from 1986 to 2010).
Phil’s humor, wisdom, music, and love of adventure and geology will never
be forgotten by the many people whose lives he touched. Throughout his
years as Denali’s geologist, Phil discovered fossils, monitored glaciers and
road hazards, reclaimed mined lands, taught geology, and predicted that if
we kept looking in the right places, someday we would find a dinosaur track
in the park.
Denali geology is no piece of cake, or one should say ‘layer cake,’
as places like the Grand Canyon are often described. In fact, I like
to describe the geology of Denali as a mix of several well-known
western parks. The recipe is to place the sediments of the Grand
Canyon, the plutonic rocks of Yosemite, and the volcanics of Mount
Rainier in a blender, and turn it on briefly to ‘chop.’ Then layer as
a parfait, and serve with large quantities of ice from the likes of
Glacier Bay National Park!
—Phil Brease
NPS Photo
Table of Contents
Part 1
From Old Rocks to Young Ice:
Entrance Area to Teklanika
Part 2
1
Dynamic Denali:
Teklanika to Toklat
29
Mount Healy
6
Where Teklanika and
Cantwell Formations Meet
32
Glacial Forces
7
Teklanika Dikes
33
Glacial Erratics
8
First Dinosaur Footprint Found In Denali
36
Drunken Trees
9
Tattler Creek
37
Hines Creek Fault Expression
10
Igloo Creek Debris Slide
40
Lignite/Dry Creek Terminal Moraine
11
Sable Pass Debris Slide
42
The High One Emerges
12
Coal Mining by the East Fork Toklat
43
Gossan
13
Polychrome Pass
44
Gravel Ridge
14
Bear Cave Slump
46
Building the Park Road
47
Pretty Rocks Landslide
48
Spheroidal Weathering
50
Polychrome Overlook—Looking North
51
Savage River
16
Nenana Gravel
18
Double Mountain
19
Antecedent Stream
23
Polychrome Overlook—Looking South
52
Drunken Forest
24
Patterned Ground
55
Kettle Ponds
25
Road-Blocking Debris Flows
58
Teklanika River and Surrounding Area
28
Toklat River
59
Part 3
A Park of Unusual Scale:
Toklat to Kantishna
Geo Features
60
Rock Types
4
Highway Pass
64
Braided Rivers
15
Bergh Lake
65
Aufeis
22
Denali Unobscured
67
Assembling Alaska: Accreted Terranes
26
Eielson Visitor Center
68
Paleontological Wonders
34
Pillow Basalt
71
Precarious Permafrost
38
Muldrow Glacier
72
Glaciers
56
Hines Creek Fault
74
Why is Denali so Tall?
70
Muldrow Moraines
75
Earthquakes
78
Western Kettle Ponds
76
Geologic Timeline
84
Wonder Lake
77
Glossary
85
Glaciofluvial Terraces
80
References
88
Seismic Activity in the Kantishna Hills
81
Index
94
Kantishna Area Mining Legacy
82
Introduction
Denali National Park and Preserve is a place where powerful geologic
forces—tectonics, volcanism, and glaciation, among others—have collectively
produced a stunning showcase of landscape features. Some features
dominate, like the flanks of Denali and the glacially-carved valleys that
surround it, while others may only be noticed by the trained eye. This
guide highlights some of the most interesting geological phenomena
that can be experienced from the Denali Park Road. It stands on the shoulders
of several past road guides, including some by the previous park geologist,
Phil Brease10,48. Though the text is composed with an east-to-west drive
in mind, each feature stands alone, allowing for the guide’s use regardless
of where you are or how you got there.
If you are new to the field of geology or to Denali, you may want to
read the GEOFeatures first, as they cover broad topics such as rock
types, how Alaska and the Alaska Range were formed, braided rivers,
paleontology, glaciers, and earthquakes. Skimming the glossary will also
make the text more understandable for those unfamiliar with geology
terminology. For readers with physical science backgrounds, be aware that
some geologic names (terranes, glaciations, and such) are capitalized in
non-conventional ways to aide comprehension for the layperson.
The text is divided into three sections that group geologically-similar areas
and roughly divide the Denali Park Road into thirds. Each section opens
with an overview map and contains mile-by-mile feature descriptions,
GEOFeatures, and fun facts.
Through this book, we invite you to celebrate 100 years of geologic
research and exploration in Denali National Park and Preserve. In 2016
and 2017, the National Park Service and Denali celebrated back-to-back
Centennials. Both birthdays honor the researchers and rangers who have
dedicated themselves to understanding and stewarding America’s special
places. We hope you enjoy exploring Denali geology through these pages
and in person, and by doing so, help us launch another 100 years of learning
and conservation.
NPS Photo / Tim Rains
PART From Old Rocks to
Young Ice
1
Park Entrance to Teklanika
For the first 30 miles, the Denali Park
Road parallels the Hines Creek Fault
while winding between the Outer
Range to the north and the foothills
of the far larger Alaska Range to the
south. This portion of the road
showcases
geologic
wonders
ranging from the oldest rocks in
the park to modern permafrost
features. The Outer Range is
composed of rocks that have been
metamorphosed
by
multiple
episodes of compression and heat.
Much more recently, glaciers carved
the valleys through which the road
winds, transported huge amounts
of debris, and left behind erratics
and other evidence of their passage.
While these particular glaciers
are now gone, the ground is still
permanently frozen beneath portions
of the taiga and tundra ecosystems
through which you will soon travel.
However, climate change is starting
to thaw Denali’s frozen ground, with
tangible impacts on trees, roads, and
infrastructure.
1
Mile Feature
0–15
Mount Healy
2.4
Glacial Forces
3–5
Glacial Erratics
3–8
Drunken Trees
7.1
Hines Creek Fault Expression
8.3
Moraine of Lignite/Dry
Creek Glacial Advance
9–13
The High One Emerges
13.5
Gossan
13.9
Gravel Ridge
14.7
Savage River
18.6
Nenana Gravel
19.7
Double Mountain
22.8
Antecedent Stream
23.5
Drunken Forest
28.8
30.2
Kettle Ponds
Teklanika River and
Surrounding Area
22
21
23
25
26
27
28
29
30
31
32
33
2
24
18
20
19
8
1
2
15
3
14
17
16
13
12
11
10
8
9
3
7
6
5
4
0
GEO
FEATURE
Rock Types
Three major types of
rocks make up Earth’s crust: igneous,
sedimentary, and metamorphic.
Igneous rocks are formed when
molten rock solidifies. When magma
cools slowly deep within the earth,
the resulting rocks—granite being
a classic example—are classified
as intrusive. When magma cools
rapidly at or near the surface, often
as lava emerging from a volcano, it is
classified as extrusive. Basalt, rhyolite,
and andesite are common types of
extrusive igneous rocks. All igneous
rocks are characterized by crystalline
structures. Intrusive rocks tend to have
large crystals, while extrusive rocks
have small, often indiscernible crystals.
Igneous rock formations described
in this guide include the Teklanika
Formation and Mount McKinley
Granite.
Below: Plant fossils in a sedimentary
rock tell us about the park’s past.
NPS Photo
NPS Photo / Tim Rains
Above: Igneous rocks give Polychrome Pass its iconic multi-hued tones.
Sedimentary rocks are derived from
sediments—particles
of
mineral
and organic material that have been
deposited by water or wind. Sediments
are commonly carried by rivers or
streams and deposited in basins such
lakes and seas. These sediments are
often buried and compressed into
rock. Typical sedimentary rocks
4
include sandstone, limestone, shale,
and chert. Fossils found in sedimentary
rocks provide clues to the environment
in which the sediment was deposited.
Sedimentary
rock
formations
described in this guide include the
Cantwell Formation, Kahiltna Flysch,
the Usibelli Group, and Nenana Gravel.
Metamorphic
rocks
are
preexisting rocks that have been
changed due to intense heat
and/or
pressure
without
completely melting. The original
rocks
can
be
sedimentary,
igneous, or even metamorphic.
When rocks are squeezed and
baked beneath Earth’s surface or
by contact with magma, minerals
may be replaced or the rock
may change texture. Typical
metamorphic rocks around Denali
include schist, slate, and marble.
The Yukon-Tanana Terrane is
the only metamorphic group of
rocks described in detail in this
guide. Four other terranes found
in Denali (see p.26) also contain
metamorphic rocks.
NPS Photo / Tim Rains
5
MILE Mount Healy
0–15 The park entrance area is
dominated by Mount Healy, which
looms just north of the park road.
Though Mount Healy is referred to
as one mountain, its ridgeline actually
extends for 15 miles (24 km) from
the George Parks Highway to the
Savage River. Mount Healy is part of
the informally named Outer Range,
which also includes Mount Margaret
and Mount Wright to the west of the
Savage River.
The foundation for the entire
Outer Range is the metamorphic
Yukon-Tanana Terrane. Terranes are
fragments of the Earth’s crust that
have been scraped or broken off of
one tectonic plate and sutured onto
another. The rocks of this terrane,
the oldest that you’ll find in the park,
formed
~400
million
years
ago
as
shallow-water
seafloor
deposits and were intruded by
igneous rocks ~365 million years
ago23,29. In the Early Jurassic Epoch
(~195 million years ago), these
rocks were accreted onto the North
American continent. Since then
the
Yukon-Tanana
rocks
have
experienced multiple episodes of
regional metamorphism3, 45.
Photo by Andrew Collins
6
The Yukon-Tanana Terrane is the
foundation for roughly the northern
third of the park and many of the
nearby mountains that line the
George Parks Highway, including
Sugarloaf Mountain northeast of the
park entrance. The Yukon-Tanana
Terrane extends northwards to the
Brooks Range and makes up the hills
surrounding Fairbanks, as well as east
into Canada56.
Below: The Mount Healy ridgeline
provides breathtaking views of the park.
MILE Glacial Forces
2 . 4 Look around and imagine
the vast amounts of ice—thousands
of feet thick and miles long—required
to shape the landforms that you see
ice-free today. As recently as 22,000
years ago, much of this area would have
been covered in glacial ice.
During the last ice age, glaciers
advanced north from the Alaska Range
into the current Nenana River valley
during four major glaciations: the
Teklanika Glaciation ~2.8 million years
ago72, the Browne Glaciation during
the mid-Pleistocene (numerical age
unknown, but >300,000 years ago27),
the Lignite/Dry Creek Glaciation
~500,000 years ago44, and the Healy
Glaciation ~65,000 years ago27,14.
From this bend in the road, look east
past the railroad trestle to where the
Nenana River flows in the distance.
Approximately 22,000 years ago, the
much younger and smaller Riley Creek
Glaciation would have terminated
here14. The terminal moraine still lies
immediately to the right (south) of the
train trestle, but is largely obscured by
vegetation. The Riley Creek Glaciation
was likely a re-advance of the more
extensive Healy Glaciation80.
The Healy Glaciation is named after
a terminal moraine south of the town
of Healy. As the glacier receded,
meltwater
that
was
dammed
behind the Healy moraine and
a
bedrock
ridge
formed
the
400-foot (122 m) deep, 11-mile
(18 km) long prehistoric Lake Moody
in the valley between Healy and the
park entrance80. Lake Moody has
long since drained, but evidence of its
existence is still apparent in unstable
landforms that cause severe problems
for the railroad, highway, and buildings
in the Nenana Canyon.
A lobe of the Healy glacier flowed
uphill from the main north-south
valley, depositing the till (glacial
sediment) that Park Headquarters at
Mile 3.4 is built on.
Below: Map of glacier extents around the park entrance during the last ice age80.
Terminal Moraine of
Riley Creek Glaciation
Denali Park Road
Lignite/Dry Creek
Glaciation
Glacial Lake Moody
Healy Glaciation
Riley Creek Glaciation
Browne Glaciation
7
MILE Glacial Erratics
3 – 5 The rock next to the sign
for Park Headquarters (Mile 3.4) is
a foreigner in Denali. It’s a glacial
erratic—a rock transported by a glacier
and often, but not necessarily, made of
material exotic to its surroundings. You
can sometimes track an erratic’s origin
based on its mineral composition.
Photo by Lian Law
On nice days you can see two more
erratics at the top of the hill to the south
behind Park Headquarters. Notice how
unusual they are in both size (more than
30 feet [10 m] wide) and shape compared
to their smooth, glacially-scoured
surroundings. Upon closer inspection,
you’d notice that the erratics are granitic.
8
However, the closest bedrock outcrop of
granite is many miles away. This means
that during the Dry Creek Glaciation
several hundred thousand years ago,
these rocks traveled many miles on a
lobe of ice and were dropped in their
present locations when the ice beneath
them melted80,11.
MILE Drunken Trees
3 – 8 In the forests on both sides of
the road, you may notice a few leaning
trees. Originally upright, some of the
trees in this area are now tipping over as
a consequence of thawing permafrost.
The trees are rooted in a shallow top
layer of soil that thaws seasonally; this
soil is referred to as the ‘active layer’.
When the permafrost underneath the
active layer thaws, the trees have very
little root depth to help them remain
upright on the newly unsupported
ground. The result is that the trees look
like they’ve had a little bit too much fun.
Drunken forests (a real scientific term!)
are often found by roadsides or lakes,
where heat is more easily transferred
into the frozen ground. Throughout
the park, black spruce is the tree species
most typically found in drunken forests
because it is tolerant of the watersaturated soils often found on top
of permafrost. While you may see a
few leaning trees here, Mile 23.5 near
the Sanctuary River provides a better
example of a drunken forest.
Right: Tipsy trees occur intermittently
along the park road to the west of Park
Headquarters.
NPS Photo / Denny Capps
9
N
MILE Hines Creek Fault
7.1 Here the road crosses
Hines Creek and travels parallel to a
regionally-important geologic feature,
the Hines Creek Fault. This fault is an
active part of the larger Denali Fault
system that arcs east-west across the
state. While the fault gets its name
from the creek, the creek itself is a
fault-controlled drainage, meaning
that it follows the path of the fault and
probably wouldn’t exist if it weren’t
for the weakened material caused by
tectonic activity.
The Hines Creek Fault trends between
the park road and the Alaska Range
foothills to the south, acting as a
boundary between two terranes—the
Yukon-Tanana Terrane to the north
and the Pingston Terrane to the south69.
Above: The Hines Creek Fault appears as a dotted red line just south of the Park
Road on this annotated USGS topographic map69.
However,
glaciations,
landslides,
stream deposition, and other geologic
processes have left the fault largely
invisible here.
Near the park entrance, visible but out
of view from the park road or any trail,
lies a recent (~1,300-year-old) scarp of
the Hines Creek Fault32. This specific
fault scarp remained unnoticed,
because vegetation obscured its
location, until 2011 when a LiDAR
(Light Detection and Ranging) survey
allowed the Earth’s surface to be
seen in intricate detail. This imagery
revealed that the fault trends directly
underneath the northern abutments
of the Riley Creek bridge on the Parks
10
Highway. Luckily this was discovered
in time for the new Riley Creek
bridge, built in 2015, to be designed to
accommodate offset from the fault.
Pa
rk
Ro
ad
Above: 2011 LiDAR image of entrance area
showing Hines Creek Fault (red arrows),
Park Road (green), and Parks Highway
(blue).
MILE Lignite/Dry Creek
8 . 3 Terminal Moraine
Here the road cuts through the terminal
moraine of the Lignite/Dry Creek
Glaciation which flowed westerly, and
uphill, from the Nenana River valley
~500,000 years ago44,80. This uphill
glacial flow illustrates the tremendous
mass and power of the parent glacier,
from which the lobe that left behind
this moraine was merely an offshoot.
The moraine is not obvious from the
ground because so much time has
passed since its deposition. Erosion and
vegetation now obscure its presence.
However the feature stands out clearly
on a digital terrain model, which is a 3D
representation of the Earth’s surface
without vegetation. It is also illustrated
in the figure on page 7.
Below: The terminal moraine of the Lignite/Dry Creek Glaciation is the low, thin ridge outlined by the orange dotted line on this 2010
IFSAR digital terrain model.
7
d
Roa
k
r
Pa
8
11
MILE The High One Emerges
9–13 Here you may catch your first
view of Denali to the southwest if the
weather is fair. White-capped and still
76 miles (122 km) away, the mountain
will appear large, but not particularly
taller than other nearby peaks.
That’s a deception of perspective; at
20,310 feet (6,190 m) Denali is over
14,000 feet (4,300 m) taller than
NPS Photo / Kaitlin Thoresen
Double Mountain and the other
mountains that you see in the
foreground.
A pullout at Mile 10.5 is the first safe
place to admire the view, and Mountain
Vista rest stop at Mile 12.6 is one of
the better places to enjoy mountain
gazing along this stretch of road. On a
12
clear day the mountain will get closer
and appear bigger until you reach
Wonder Lake, where the summit
will only be 26 miles (42 km) away…
but remember, that’s as the crow
flies. It takes most of the few, hardy
mountaineers who climb Denali
starting from Wonder Lake each year a
month to make the round trip.
MILE Gossan
13.5 The orange rock outcrop
on the hill just north of the road
is called a gossan. The coloring
is caused by oxidization of ironsulfide minerals within YukonTanana rocks—rust! Outcrops
like this one oxidize into
eye-catching hues when exposed to
surface conditions and attract the
attention of prospectors looking
for gold, silver, lead, zinc, and
other
economically
valuable
resources because gossans often
indicate the upper part of ore
deposits. This particular area was
worked by prospectors, possibly
in the 1920’s and 1930’s, but was
eventually abandoned13.
NPS Photo / Daniel Leifheit
13
MILE Gravel Ridge
13.9 Just across the Savage River
to the west is a mid-valley ridge with
exposed sediment at the northern end.
The genesis and evolution of this
ridge and its surroundings is a point
of ongoing research. Some have
interpreted it to be an esker, which is
a deposit from a stream running under
or through a glacier11. Others have
interpreted it as a remnant moraine of
the Lignite/Dry Creek glacial advance
from about 500,000 years ago 44,80.
LiDAR data collected in 2005, which
measured the topography of this area
in far greater detail than any previous
survey, has revealed that the gravel ridge
and its surrounding features may have
been truncated by tectonics after having
been shaped by glaciers. Specifically,
recent faulting may have caused linear
striations in the stream sediments6.
Ultimately these landforms are the
result of several geologic processes
interacting through time. The evolution
of this story illustrates how modern
technologies such as LiDAR are casting
new light on old geologic mysteries
here and elsewhere in the park.
Right: Lineations (red arrow) possibly
indicate tectonic shaping of the area.
The exposed sediment in the photo
below is located near the upper left of
this digital terrain model (blue arrow).
Below: The mid-valley ridge in the
Savage River braidplain is visible at the
bottom of the photo.
NPS Photo / Kaitlin Thoresen
14
Par
kR
oad
GEO
FEATURE
Braided Rivers
Many of the rivers
and streams in Denali are braided,
consisting of many short-lived channels
weaving across a wide bed of cobbles,
gravel, sand, and silt. What you are
seeing is not just a “dry phase”—water
almost never flows over the entire
width of a braided river at any one
time. Braided rivers and streams occur
within watersheds where relatively
large amounts of sediment are
transported
by
relatively
small
amounts of water. Because glaciers
are such powerful agents of erosion
and therefore create large amounts of
sediment, braided rivers are classically,
although not exclusively, glacially-fed.
At higher water levels, braided rivers
can transport larger amounts of
sediment from upstream, but they
deposit that sediment when the water
level drops and slows. The deposited
sediments force the water to move to
new paths of less resistance. In Denali,
this often happens on a diurnal basis,
Below: The braids of an unnamed stream weave through Denali’s lush landscape.
Photo by Diane Kirkendall
15
with higher water flows and sediment
transport occurring during the heat of
the day when snow and ice is melting
and contributing to flow, but it also
varies seasonally and in response to
storms and glacial processes.
Watch for river braids as you cross
the Savage (Mile 14.7), Teklanika
(Mile 30.2), and Toklat (Mile 53) rivers,
from Polychrome Overlook (Mile
45.8), and from Eielson Visitor Center
(Mile 67), among other locations.
NPS Photo / Tim Rains
MILE Savage River
14.7 Savage River is one of several
braided rivers in Denali that are
characterized by transitory channels
meandering across wide beds of
sediment over time. However this
behavior is not the result of glacial
melt, as is the case for most braided
rivers in the park, because no glaciers
remain in the Savage River watershed.
Savage River is braided because of
high sediment input from brittle rock,
and from a relative lack of vegetation
stabilizing its headwaters.
An important transition zone that
illustrates the glacial history of this
area is located about halfway between
the Savage River vehicular bridge and
the Savage River Loop Trail footbridge
to the north. Upstream (south) from
this point, Savage River runs wide and
shallow in a U-shaped valley typical
of glacial scouring. Downstream
(north), Savage River runs fast and
restricted through a V-shaped valley
typical of river erosion. Look for these
distinctive shapes as you cross the
16
vehicular bridge11. While more
extensive glaciations have affected
the topography of the canyon in the
past, they occurred over two million
years ago27.The river has therefore
had substantial time to erode the
V-shaped canyon that we see today.
Above: The view south from the
Savage River vehicular bridge in
the fall. This portion of the river flows
through a valley shaped by past
glaciations.
Left: The view north from the Savage
River vehicular bridge shows a V-shaped
valley resulting from river erosion. This
topography is different from the glaciallysculpted terrain seen on page 16.
FUN FACT: Savage Rock (photo
below), the jagged outcrop that
you can walk to just uphill from
the Savage River parking lot, is
a surprising stumper. Why this
outcrop is so prominent compared
to its surroundings—despite being
made of similar rocks—remains a
mystery. One theory is that faulting
caused the rock to protrude from the
surrounding topography. A second
is that it slid down from above. Or
Savage Rock could be made of more
resistant schist than the surrounding
metamorphic rock. Further studies
are needed to resolve this enigma.
NPS Photo / Tim Rains
The Savage River canyon is one of the
few places where erosion has exposed
the Yukon-Tanana Terrane bedrock
along the road. Take a closer look
and you’ll notice large amounts of
mica-quartz schist, a shiny rock that
gets its sparkle from the flaky mineral
sericite and quartz veins. The varieties
of metamorphic rock in the YukonTanana Terrane, along with the degree to
which they have been folded and
faulted, attest to the terrane’s age and
dynamic history.
Photo by Diane Kirkendall
17
NPS Photo / Lian Law
MILE Nenana Gravel
18.6 The
Alaska
Range
experienced the majority of its
uplift in the last six million years.
Scientists have deduced the timing
of this impressive tectonic episode
partially thanks to the humble Nenana
Gravel formation that outcrops here
on the north side of the road. The
Nenana Gravel is a ~4,000-foot thick
(1,200 m) sedimentary formation
composed
mostly
of
looselyconsolidated gravel and sand. These
sediments are from igneous and
sedimentary parent rocks that match
the lithology (physical characteristics)
of rocks in the Alaska Range. The
Nenana Gravel formation is often
underlain by a ~2,000-foot thick
(600 m) group of sedimentary
formations called the Usibelli Group,
the sediments from which match
parent rocks from the metamorphic
Yukon-Tanana Terrane to the north61.
The fact that the Nenana Gravel
overlies the Usibelli Group in the
Tanana Basin—a large, low area on the
north side of the Alaska Range—is one
of the primary ways that scientists know
when the uplift of the Alaska Range
began. Leaf fossils, pollen, radiometric
dates, and tectonic evidence from the
two formations demonstrate that the
Usibelli Group sediments washed
into the Tanana Basin from the north
mostly during the Miocene Epoch
(5–23 million years ago). Around six
million years ago, these sedimentary
layers started being buried by Nenana
Gravel sediments flowing in from the
south. This shift in sediment source
indicates when the Tanana Basin was
tilted north by the newly rising Alaska
Range61,75. Sediment deposits continue
to accumulate in the Tanana Basin
today as the Alaska Range continues to
rise.
18
Above: A park shuttle bus approaches a
Nenana Gravel outcrop to the west of
the Savage River. The summit of Denali
peeks out from behind the ridge on the
left.
FUN FACT: The Usibelli Group of
formations is mined for coal 11 miles
(18 km) north of the park entrance
near the town of Healy. The lignite
coal dates to the Miocene and is
evidence of a time when Denali’s
environment consisted of swampy
bogs and vast forests, a drastic
departure from today’s boreal forest
and alpine tundra41! The Usibelli Coal
Mine is currently the only active coal
mine in the state. The coal, notable for
its low sulfur content, is transported
to power plants in interior Alaska
as well as exported to South Korea
and Chile78.
MILE Double Mountain
19.7 To the south lies the broad
north slope of a mountain with a
jagged, indistinct summit—Double
Mountain. The mountain is capped
by the colorful Teklanika Formation,
a Tertiary (55–60 million years ago)
volcanic rock unit21. The base of
Double Mountain is composed of the
Cantwell Formation, a late Cretaceous
(~70 million years ago) sedimentary
rock unit, and is intruded by the
overlying Teklanika Formation21.
It is noteworthy that the Teklanika
Formation rocks are similar in age
and mineral composition to those of
the Mount McKinley Granite, which
comprises many of the highest peaks
in the Alaska Range, including Denali.
The two rock units have very different
appearances because the volcanic rocks
cooled relatively quickly at the surface
and therefore have a finer texture, while
the granitic rocks cooled very slowly
many miles deep in the crust and have
a relatively coarse crystalline structure.
The Teklanika volcanic eruptive
center was near Denali’s peak, as
demonstrated by the direction that
the volcanic conglomerate flowed.
This directionality is interpreted by
researchers based on the orientation
of clasts, or fragments, in the
conglomerate. Some of the Teklanika
clasts are enormous (40 feet or 12 m
across), and were violently erupted out
of a volcano during an event similar
to the Mount St. Helens eruption of
1980 (figure p.21). Also visible is a
whitish tuff, or ash layer, dipping at an
angle near the upper third of Double
Mountain. This 30-foot (9 m) thick
tuff is the result of many thinner ash
deposits accumulating over time20.
NPS Photo / Russell Rosenberg
NPS Photo / Russell Rosenberg
Above: A sample of McKinley Granite,
an intrusive rock.
Above: A sample of Polychrome
rhyolite, an extrusive or volcanic rock.
NPS Photo / Lian Law
Above: Double Mountain (left) looks shaded in the early morning light while Denali looks pinkish and hazy in the background.
19
Left: Diagrams showing the depositional
and tectonic history of the Denali area
before, during, and after Teklanika
volcanism20.
A Late Cretaceous
River drainage
Paleoflow
Proto Alaska Range
N
Paleozoic rocks
Cantwell Formation
A) The Cantwell Formation was deposited
into the Cantwell Basin on the north side
of the Alaska Range ~70 million years
ago (late Cretaceous) during a time of
active tectonics.
B) Teklanika volcanic rocks erupted
from the southwest of their present
location 55–60 million years ago and
were deposited on top of the Cantwell
Formation.
B Late Paleocene
Future Denali Fault
Paleoflow
Eruptive center
magma chamber
(future Alaska
Range granite)
Debris
Avalanche
Pyroclastic
Flow
Lava
Teklanika Formation
C Post-Early Eocene
Denali Fault
Remnant volcanoes
Alaska Range
granite
Right-lateral offset and
uplift of eruptive center
20
C) Subsequent right-lateral strikeslip movement along the Denali Fault
then displaced the Teklanika rocks to
the northeast relative to their eruptive
center. The McKinley pluton (comprised
of Mount McKinley Granite) may
represent the uplifted roots of the
Teklanika eruptive center.
Crater
Area
5 km
N
From Voight et al. 1981; USGS Prof. Paper 1250
Photo by Lyn Topinka
NPS Photo / Lian Law
Above: This large boulder (inset left) is a clast, or fragment, on Double Mountain (main photo) that is thought to have been
deposited by volcanic mud that flowed out of the Teklanika eruptive center. Similar mudflows deposited huge boulders (inset
right) far from the volcanic vent of Mount St. Helens during its 1980 eruption20.
21
NPS Photo / Sierra McLane
GEO
FEATURE
Aufeis
Depending on when
you visit, you may see flows of ice
along the park road that formed in the
winter. Called aufeis or overflow, this
ice usually forms in Denali when very
cold temperatures freeze surface water,
thereby sealing in the groundwater
below. Over time (minutes to days),
pressure builds up until the surface
ice cracks and the groundwater flows
upward onto the surface, creating a
new ice layer on top.
Overflow events occur repeatedly
throughout Denali’s long winters,
building up ice layers to depths of six
feet (2 m) or more. This phenomenon
is limited to high-latitude areas.
While often occurring in the same
places annuall